MICHAEL RATNER, as a law student at Columbia University, was pushed to the ground and beaten by the police in 1968 as he and other students blocked the entrance to a building occupied by protesters.

This would turn out to be one of those defining moments. Mr. Ratner, who would graduate second in his class, got up, looked at his bloodied fellow protesters and decided to become a rebel.

“That night was crucial,” he said. “An event like this created the activists of the next generation. I never looked back. I decided I was going to spend my life on the side of justice and nonviolence.”

Three decades later, he is still at it.

Mr. Ratner, 59, is president of the Center for Constitutional Rights, a nonprofit organization that litigates civil and human rights cases. He has worked or been affiliated with the advocacy group since graduating from law school.

Most recently, Mr. Ratner suffered a setback on a petition seeking a writ of habeas corpus on behalf of two British and Australian detainees, alleged members of Al Qaeda, being held at Camp X-ray, at Guantanamo Bay in Cuba. A judge ruled on Wednesday that United States courts had no jurisdiction over prisoners there; the center said it would appeal.

Mr. Ratner said the decision was troubling. “But we are going to pursue it,” he said. “It is an important case and an incredibly important principle.”

The center has also taken up the cause of Muslims being detained indefinitely in the United States in the wake of the Sept. 11 attacks. In the past, the center has defended causes as varied as the right of street artists to peddle outside the Metropolitan Museum of Art and challenged the firing or demotion of African-American and Latino teachers who failed to pass a newly instituted state teacher exam.

“The assault on civil liberties is as bad as I have ever seen it,” Mr. Ratner said while seated in his cramped offices in Greenwich Village, “and it is not like the 60’s or 70’s when there were people fighting for civil rights and ending the war in Vietnam.

“What we have now is a frightened population. The government is able to push through draconian laws that are in clear violation of the Constitution. These are the most sweeping changes of our fundamental rights in over 50 years.”

The government’s open-ended war on terror has, in the eyes of Mr. Ratner and his supporters, condemned the United States to a downward spiral. This struggle, he said, has left him watching while many of the changes he and other liberals fought for over the last few decades have been reversed. And, he says, especially if there is another terrorist attack, things will get worse.

“A permanent war abroad means permanent anger against the United States by those countries and people that will be devastated by U.S. military actions,” he said. “Hate will increase, not lessen; and the terrible consequences of that hate will be used, in turn, as justification for more restrictions on civil liberties in the United States.”

He ticks off a list of things that worry him, including increased censorship of information, the silencing of dissent, ethnic and religious profiling, the decision to wiretap lawyers and their clients without a court order, and the creation of military tribunals that can mete out the death penalty without appeal.

“The laws they said would only apply to immigrants are now being applied to ordinary citizens,” he said. “The military tribunals were set up to detain noncitizens. And now two citizens have been picked up and are being detained infinitely without any right to a court process.”

But perhaps what is as depressing for Mr. Ratner is watching the gains of a lifetime drain away.

“I keep going with the individual human rights cases, such as that against the general that massacred people in East Timor, but it is not the same sense of a struggle that will change things. You get to the point where you have a very conservative government and you feel like you are a flickering light.

“But we have to keep the light lit. There will be, one day, a disbelief among people . They will not understand how we allowed 5,000 people to be rounded up in our own country or how we held thousands of prisoners without honoring the Geneva Convention.”

HE said he still found delight in all battles, big and small. He pushes his two children to dissent and proudly explained that his daughter petitioned the Parks Department to change the swings in the local park from baby swings to children’s swings. He just read “The Count of Monte Cristo,” “a man who was jailed for no reason and went out and got revenge,” to his son.

His wife of 16 years, Karen Ranucci, runs a nonprofit group that distributes Latin American videos to universities and educational institutions and works for “Democracy Now,” a syndicated radio and television program. They live in Greenwich Village.

When he is not tilting at windmills, he is fly-fishing in streams in upstate New York or exploring the foundations of old houses in the woods. As a boy growing up in Cleveland, he dreamed of being an archaeologist.

“I love the past,” he said. “I love looking at archaeological items. I have taken my kids to every ruin in Rome. We go on digs in Central America. I used to think it wasn’t political, but it turns out to be highly political. After all, what layer of civilization do you save?”